1. Field of the Invention
The present invention relates generally to image forming apparatuses, and more particularly, to an image forming apparatus which permits a user to determine whether desired image formation can be achieved when the user sets a set of documents.
2. Description of the Related Art
There has been known an image forming apparatus capable of making time display associated with image forming processing, such as an apparatus disclosed by Japanese Patent Laying-Open No. 57-70553. Since the image forming apparatus can display the time when a copying operation for a set of a plurality of documents is completed, the user may confirm the display, then leave the image forming apparatus and return around the time of the completion of the set copying operation. More specifically, the user can make effective use of the time period until 1 the copying operation by the image forming apparatus completes.
The above-described image forming apparatus, though displays the time of the completion of a copying operation, does not take into account such a case in which the operation of the image forming apparatus is interrupted because of some error before the completion time, and the set copying operation cannot be completed as a result.
If, for example, the user is away from the image forming apparatus after a copying operation is initiated, and a paper empty state is attained before the displayed completion time, the copying operation will not have been completed when the user returns to the image forming apparatus at the displayed completion time.
Meanwhile, there is known an image forming apparatus including a memory for storing image data which reads all the data of a set of documents and then starts printing. For example, an apparatus disclosed by U.S. Pat. No. 5,253,077 reads documents while storing the image data into its memory, and at the same time sequentially reads out data stored in the memory while printing the data.
In such an image forming apparatus, once a document is read and stored in the memory, the operator can leave the apparatus with the document as soon as the document has been read (if a printing operation thereof is not completed), because the printing operation is performed based on the image data stored in the memory.
In this case, during printing, sheets of paper set in a paper feeding cassette are sequentially fed for printing. A known apparatus is provided with another paper feeding cassette accommodating paper sheets of the same size, direction and attribute as the other cassette to cope with the case in which the other paper feeding cassette runs out of paper sheets (hereinafter the case will be referred to as "paper empty"), and continues an ongoing printing operation by switching between the paper feeding cassettes, so that more sheets of paper than the volume of each paper feeding cassette is available.
In some recent image forming apparatuses, the power supply is automatically turned off after the apparatus is left not operated for a prescribed time period, in other words measures to cope with the energy restriction is taken.
Although the above-described image forming apparatuses are provided with a number of paper feeding cassettes and switch between the cassettes in response to paper empty, there is still the possibility of paper empty if a large volume of copies are to be made. In particular, if the user leaves the apparatus with documents as soon as the documents have been read, the operator are usually not aware of paper empty if any.
In addition, if the operator is not aware of paper empty for a long period of time, and no operation is performed, the power supply of the image forming apparatus is automatically cut off to cope with the energy restriction, and data read and stored in the memory will be erased. Therefore, the same documents should be again read for storage, resulting in poor operability.
In this case, there may be a resuming function to hold data stored in the memory, and return the data to the memory once the power supply is again turned on after the interruption, but another power supply should be separately provided, which considerably increases the cost. Furthermore, the duration of keeping the data "resumable" is limited.
Some facsimile having an intercepting function performs memory intercepting, in other words allows data to be stored in a memory outside the apparatus if the facsimile on the receiving side is in the state of paper empty. There are other apparatuses which output data to another predetermined facsimile if the facsimile the data is destined for is in a busy state.
The method of simply allowing data to be stored in a memory outside the apparatus cannot solve the problem of the destruction of the content of a job when the power supply off mode is entered. The method of outputting data to a facsimile at another location necessitates the user to move to that location in every such case. In addition, the facsimile of the destination and the intercepting facsimile both should be maintained, which is cumbersome.